Metal recovery reactor and metal recovery system

ABSTRACT

The present invention relates to a metal recovery reactor and a metal recovery system. The metal recovery device according to the present invention comprises an electrolytic cell which receives a solution containing metal ions from the outside, and which reduces and precipitates the metal ions of the solution on the surface of a cathode when the solution is supplied to a reaction space formed between an anode and the cathode surrounding the anode. The cathode comprises a main cathode and an auxiliary cathode positioned inside the main cathode and capable of being detached and attached from the main cathode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reactor for recovering metal and asystem for recovering metal that can rapidly metal fast using anelectrolyzer.

2. Related Art

Valuable metals are usually contained in wastewater, plating wastewater,or washing water produced in the electronic industry including asemiconductor manufacturing process. In particular, a considerableamount of precious metals are contained in wastewater or washing waterproduced in industrial processes using those precious metals, so thereis a need for recovering and recycling them.

Precious metals in wastewater or washing water are generally recoveredby an ion exchange method, an activated carbon method, andelectrowinning, and the liquid after recovering is neutralized and thenthrown out or purified and then reused.

The electrowinning is a method of performing electric reduction on awater solution or an extracting solution containing precious metals intoan electrolyte and then extracting desired precious metals on a cathode.The electrowinning can obtain high-purity metals at a time withoutundergoing a crude metal and can reuse a solvent for extracting becauseit is recycled in accordance with electrolysis.

However, despite those advantages, the electrowinning is easy to beapplied when the concentration of metal ions in a water solution ishigh, and when the concentration is low, metal ions slowly move to thesurface of a cathode, so the recovery rate decreases.

DOCUMENTS OF RELATED ART Patent Document

Korean Patent Application Publication No. 2012-0138912 (published onDec. 27, 2012)

SUMMARY OF THE INVENTION

The present invention provides a reactor for recovering metal and asystem for recovering metal that can rapidly recover metal using anelectrolyzer.

In an aspect, a reactor for recovering metal is provided. The reactorincludes an electrolyzer that receives a water solution containing metalions from the outside and reduces and extracts metal ions in a watersolution on the surface of cathodes, when the water solution is suppliedinto a reaction space between an anode and the cathodes surrounding theanode, in which the cathodes include a main cathode and a sub-cathodedisposed inside the main cathode and separable from the main cathode.

The reduction and extraction of the metal ions may occur on the innerside of the sub-cathode.

The main cathode may have a ring shape and the sub-cathode may have aplate shape and may be wound inside the main cathode.

The sub-cathode may be made of a material that is dissolved by acid thatdoes not dissolve metal to be recovered.

The sub-cathode may be in close contact with the main cathode and maysubstantially fully cover the inner side of the main cathode.

The anode may be formed in a bar shape and may have a plurality ofgrooves on the outer side.

The anode may be a hollow part with both ends open and the side of theanode may not be open.

The ratio of the surface area of surface area/cathode of the anode inthe reaction space may be larger than 1.

In another aspect, a system for recovering metal is provided. The systemincludes: a reservoir that keeps a water solution containing metal ions;and an electrolyzer that receives a water solution containing metal ionsfrom the outside and reduces and extracts metal ions in a water solutionon the surface of cathodes, when the water solution is supplied into areaction space between an anode and the cathodes surrounding the anode,in which the cathodes include a main cathode and a sub-cathode disposedinside the main cathode and separable from the main cathode.

The sub-cathode may substantially fully cover the inner side of the maincathode in close contact with the main cathode, and the reduction andextraction of the metal ions may occur on the inner side of thesub-cathode.

The sub-cathode may be made of a material that is dissolved by acid thatdoes not dissolve metal to be recovered.

The anode may be formed in a bar shape and may have a plurality ofgrooves on the outer side.

The anode may be a hollow part with both ends open and the side of theanode may not be open.

The ratio of the surface area of surface area/cathode of the anode inthe reaction space may be larger than 1.

The system may further include a solid-liquid separator that receives awater solution discharged from the electrolyzer and separates metalparticles.

The system may further include: an assistant tank that is disposedbetween the electrolyzer and the solid-liquid separator; and acontroller that reduces a water solution supplied to the electrolyzerwhen the level of the assistant tank is a first level or more, and thatreduces a water solution supplied to the solid-liquid separator when thelevel of the assistant tank is a second level, which is smaller than thefirst level, or less.

According to the present invention, there are provided a reactor forrecovering metal and a system for recovering metal that can rapidlyrecover metal using an electrolyzer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the configuration of a system forrecovering metal according to a first embodiment of the presentinvention.

FIG. 2 is a diagram illustrating a control architecture of the systemfor recovering metal according to the first embodiment of the presentinvention.

FIG. 3 is a cross-sectional view of an electrolyzer according to thefirst embodiment of the present invention.

FIG. 4 is a schematic exploded perspective view of the electrolyzeraccording to the first embodiment of the present invention.

FIG. 5 is a view showing the shape of an anode of the electrolyzeraccording to the first embodiment of the present invention.

FIG. 6 is a view showing the configuration of a cathode according to thefirst embodiment of the present invention.

FIG. 7 is a view showing assembling of the cathode according to thefirst embodiment of the present invention.

FIG. 8 is a perspective view showing an assembly of the electrolyzeraccording to the first embodiment of the present invention.

FIG. 9 is a cross-sectional view taken along line IX-IX of FIG. 8.

FIG. 10 is a flowchart illustrating an operation method according to thelevel of an assistant tank in the system for recovering metal accordingto the first embodiment of the present invention.

FIG. 11 is a flowchart illustrating an operation method for washing asolid-liquid separator in the system for recovering metal according tothe first embodiment of the present invention.

FIGS. 12 and 13 are graphs showing a recovery behavior according to ananode/cathode area ratio.

FIG. 14 is a view showing the configuration of a cathode according to asecond embodiment of the present invention.

FIG. 15 is a view showing the configuration of a cathode according to athird embodiment of the present invention.

FIG. 16 is a view showing the configuration of a cathode according to afourth embodiment of the present invention.

FIGS. 17 and 18 are graphs showing recovery behaviors according to thematerials of an anode.

FIG. 19 is a graph showing recovery behaviors according to appliedcurrents.

FIG. 20 is a graph showing recovery behaviors according to flow rates.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a reactor for recovering metal and a system for recoveringmetal according to the present invention will be described withreference to accompanying drawings.

FIG. 1 is a diagram illustrating the configuration of a system forrecovering metal according to a first embodiment of the presentinvention and FIG. 2 is a diagram illustrating a control architecture ofthe system for recovering metal according to the first embodiment of thepresent invention.

The system for recovering metal includes an electrolyzer 100 (reactorfor recovering metal), an assistant tank 200, a solid-liquid separator300, and a reservoir 400. There are provided pumps 501 and 502 andvalves 601, 602, 603, and 604 for transporting and blocking a watersolution containing metal ions and/or metal particles to be recovered(hereafter, referred to as ‘water solution’). Further, there areprovided a level measurer 210 for measuring the level of the assistanttank 200 and a timer 800 for measuring the operation time of thesolid-liquid separator 300, and the system includes a controller 700that controls operation of the pumps 501 and 502 and the valves 601,602, 603, and 603 on the basis of signals inputted from the levelmeasurer 210 and the timer 800.

The electrolyzer 100 receives a water solution from the reservoir andtakes (recovers) metal from the water solution using cycloneelectrowinning method. The electrolyzer 100 will be described in detailagain.

The assistant tank 200 receives the electrowon water solution from theelectrolyzer 100. The assistant tank functions as a buffer between theelectrolyzer 100 and the solid-liquid separator 300 and solves problemswith operational stability that may be caused by a flow rate differencebetween the first pump 501 and the second pump 502. The assistant tank200 has a level sensor 210 and the level sensor 210 senses whether thelevel of the assistant tank 200 is within an appropriate range, over anupper limit, or under a lower limit. The level sensor 210 may beachieved using various ways, such as using the entire weight or pressureof the assistant tank 200.

The solid-liquid separator 300 separates granular metal from a watersolution. The granular metal may be produced, when metal electrowon bythe electrolyzer 100 grows and divided. The solid-liquid separator 300,though not limited, may include a filter capable of separatingparticles.

The water solution with metal particles separated by the solid-liquidseparator 300 is sent back into the reservoir 400.

A water solution containing metals to be recovered which is suppliedfrom plating process etc. and a water solution with metals recoveredthrough the electrolyzer 100 and the solid-liquid separator 300 aremixed in the reservoir 400. In another embodiment, the water solutionpassing through the electrolyzer 100 and the solid-liquid separator 300may be treated through additional equipment/process without being mixedwith the water solution supplied from plating process etc.

The system for recovering metal further includes a washing unit capableof washing the solid-liquid separator. The washing unit is composed of awashing water supplier, valves 603 and 604, a washing water discharger,and a washing water line.

The electrolyzer 100 according to the first embodiment of the presentinvention is described in detail with reference to FIGS. 3 to 9.

FIG. 3 is a cross-sectional view of an electrolyzer according to thefirst embodiment of the present invention, FIG. 4 is a schematicexploded perspective view of the electrolyzer according to the firstembodiment of the present invention, FIG. 5 is a view showing the shapeof an anode of the electrolyzer according to the first embodiment of thepresent invention, FIG. 6 is a view showing the configuration of acathode according to the first embodiment of the present invention, FIG.7 is a view showing assembling of the cathode according to the firstembodiment of the present invention, FIG. 8 is a perspective viewshowing an assembly of the electrolyzer according to the firstembodiment of the present invention, and FIG. 9 is a cross-sectionalview taken along line IX-IX of FIG. 8.

Referring to FIGS. 3 to 9, the electrolyzer 100 according to the presentinvention includes an electrolytic cell 10, cathodes 20 and 22, and ananode 30.

The electrolytic cell 10 is a part for providing a space for anelectrowinning process to be described below. In the embodiment, theelectrolytic cell 10 is formed in a cyclone shape and has a body 11 anda conical part 15.

In the embodiment, the body 11 is formed in a cylindrical shape and hasa uniform diameter from the top to the bottom. An inlet 12 is formed ata side of the body 11, through the inner side and the outer side so thata water solution to be described below can flow inside. An inlet port 13guiding a water solution to the inlet 12 is connected to the inlet 12.Further, a connection hole 14 is formed at a side of the body 11 so thata wire for supplying power to the cathodes 20 and 22 to be describedbelow can be inserted.

In the embodiment, the conical part 15 extends from the bottom of thebody 11 and has a diameter gradually decreasing as it goes down, so ithas an entirely conical shape. An outlet 16 for discharging the watersolution in the body 11 is formed at the bottom of the conical part 15.Further, an outlet port 17 for discharging a water solution to theoutside is connected to the outlet 16.

Further, a sealing cap 18 for opening/closing the internal space of thebody 11 is provided. That is, female threads are formed around the innerside of the upper portion of the body 11 and male threads are formedaround the outer side of the sealing cap 18, so the sealing cap 18 isthread-fastened to the body 11. An O-ring 18 a is disposed between thesealing cap 18 and the body 11 and ensures sealing.

An insertion hole 18 b is formed through the top and the bottom of thesealing cap 18 and the anode 30 having a bar shape to be described belowis inserted in the insertion hole 18 b. The O-ring 18 c is disposed tosurround the insertion hole 18 b, so it prevents unsealing between theanode 30 and the insertion hole 18 b, which will be described below. Apressing cap 19 is thread-fastened to the upper portion of the sealingcap 18 to increase sealing by pressing the O-ring 18 c to the top of thesealing cap 18. A through-hole 19 c is formed also at the center of thepressing cap 19, so the anode 30 can be fitted therein.

The structure of the cathodes according to an embodiment of the presentinvention is described.

The cathodes 20 and 22 have an overall cylindrical shape and are fittedinside the body 11. In the embodiment, the cathodes 20 and 22 are formedin an overall cylindrical shape having a uniform diameter from the topto the bottom.

The cathodes 20 and 22 include a main cathode 20 and a sub-cathode 22.The main cathode 20 has a cylindrical shape. The sub-cathode 22 has aplate shape and bends inside the main cathode 20 in assembly.Accordingly, in the embodiment, the main cathode 20 and the sub-cathode22 are not physically combined and can be separated at any time, ifnecessary.

An inlet 21 of the main cathode 20 is formed at a position correspondingto the inlet 12 of the body 11 and communicates with the inlet 12 of thebody 11. A sub-inlet 23 corresponding to the inlet 21 of the maincathode 20 is formed also at the sub-cathode 22. A water solutioncontaining metal ions flows into the cathodes 20 and 22 through theinlet 12, the inlet 21, and the sub-inlet 23.

In the embodiment, a water solution is required to flow into thecathodes 20 and 22 and generate a turbulent flow, and for this purpose,the flow direction of the water solution flowing into the cathodes 20and 22 is required to substantially be the direction of a tangent lineof the cylindrical cathode. That is, assuming that the cylindricalcathode is a circle, it should be flow inside in the tangentialdirection at the edge of the circle. The water solution can generate aturbulent flow while rotating along the inner side of the cathodes 20and 22, only when it flows inside in the tangential direction.

For example, when the water solution flows inside radially toward thecenter of the cathode, turbulence is not generated in the electrolytecell 10, so a desired effect cannot be obtained.

The main cathode 20 is electrically connected with a power through theconnection hole 14 of the body 11. The main cathode 20 and thesub-cathode 22 are electrically connected in close contact with eachother and the sub-cathode 22 is connected to the power through the maincathode 20.

The sub-cathode 22 substantially fully covers the inner side of the maincathode 20, in close contact with the main cathode 20. Accordingly,reduction and extraction of metal ions concentrate on the inner side ofthe sub-cathode 22. Little or substantially no reduction and extractionof metal ions may occur on the inner side of the main cathode 20.Further, metal ions are little reduced and extracted on the outer sideof the sub-cathode 22 too.

It is possible to prevent unnecessary reduction and extraction bycoating the inner side of the main cathode 20 and the outer side of thesub-cathode 22, where metal ions are little reduced and extracted, withTeflon.

As an electrowinning process is performed, metal to be recovered isextracted on the inner side of the sub-cathode 22. After the process,the sub-cathode 22 is easily separated from the main cathode 20 and apost process for separating metal to be recovered such as gold from thesub-cathode 22 is performed. When metal that is dissolved in acid isused for the sub-cathode 22, precious metals such as gold or platinumare not dissolved, but only the sub-cathode 22 is dissolved in an acidsolution, so precious metals can be easily separated from the cathode.The sub-cathode 22 may be made of, for example, iron, zinc, tin, nickel,or copper.

The main cathode 20 may be made of a material different from thesub-cathode 22, for example, stainless steel or titanium.

As described above, since the sub-cathode 22 is not physically combinedwith the main cathode 20, it can be easily inserted inside the maincathode 20 and separated after processes. Accordingly, the metal on thesurface can be recovered by separating only the sub-cathode 22 afterprocesses. It is possible to start a new process by inserting only a newsub-cathode 22 with the main cathode 20 remaining. Further, since metalis little extracted on the main cathode 20, work such as washing iseasy.

On the other hand, when the extraction amount of metal to be recoveredincreases, the extracted metal can be separated in particles and theseparated metal particles are separated by the solid-liquid separator300. Further, metal having a feature of dendritic growth is easilyseparated from a cathode and separated by the solid-liquid separator300.

The anode 30 is formed in a long bar shape and inserted in theelectrolyte cell 10 through the through-hole 19 c of the pressing cap 19and the insertion hole 19 b of the sealing cap 18. The top of the anode30 is electrically connected with the power.

The anode 30 is a hollow part, so the inside of the electrolytic cell 10communicates with the outside through the hollow portion of the anode30. A water solution in the electrolytic cell 10 falls to the conicalpart 15 and then, some of the water solution is discharged outsidethrough the outlet 16 at the bottom of the conical part and the other isdischarge outside through the anode 30.

A plurality of grooves 32 is formed on the outer side of the anode 30.The grooves 32 circumferentially formed with regular intervals on theanode 30 and have the same width ‘d’ and gap ‘c’. The grooves 32increase the surface area of the anode 30. The grooves 32 can be formedat a lower cost than through-holes. Forming the grooves 32 is for easilyincreasing the surface area of the anode 30 in comparison with formingthrough-holes. Increasing the surface area of the anode 30 by formingthe grooves 32 influences a recovery efficiency, which will be describedbelow.

The surface area of the anode 30 can be adjusted by changing the width‘d’, gap ‘c’, and depth ‘y’ of the grooves 32.

The grooves 32 can be changed in various arrangements and shapes. Inanother embodiment the grooves 32 may have different widths ‘d’ and maybe formed with irregular intervals. Further, the grooves 32 may beformed in the longitudinal direction of the anode or may be formed inthe shape of lattices. The cross-section of the grooves 32 may bevariously changed such as in a trapezoid or a semicircle, not arectangle as in the embodiment.

In the embodiment, the anode 30 may be made of titanium, in which thestrength is increases by coating the titanium with an iridium oxide. Theanode formed by coating titanium with an iridium oxide stably remains ina strong acid solution or a strong alkali solution without be dissolved.Further, the anode 30 may be made of stainless steel, in which thestainless steel may be coated with platinum.

The electrowinning process generally requires high decompositionvoltage, and when overvoltage is applied with graphite used as an anode,the surface of the graphite anode weakens and it is worn by high-speedliquid in many cases. However, as in the embodiment, when an electrodeformed by coating titanium with an iridium oxide or an electrode formedby coating stainless steel with platinum is used, it is not worn even athigh overvoltage and a high flow speed due to its own mechanicalstrength and maintained the original shape, so stability is high.

The reason that the electrolyzer 100 according to the present inventioncan effectively recover metal even at low concentration of metal ionshas been explained in detail in Korean Patent Application PublicationNo. 2012-0138921 invented by the inventors of present application.

A method of recovering metal using the system for recovering metaldescribed above is described hereafter.

A water solution in the reservoir 400 is supplied to the electrolyzer100 by the first pump 501. In detail, it is supplied to the electrolyzer100 through the inlet 12 of the electrolyzer 100. Power is connected tothe cathodes 20 and 22 and the anode 30 of the electrolyzer 100.

The water solution is sent into the electrolyzer 100 at an inflow speedof 2˜20 m/sec. When it is sent at a speed less than 2 m/sec, it cannotgenerate a turbulent flow in the cathodes, so desired result cannot beachieved, and when the speed is larger than 10 m/sec, it is noteconomical.

The water solution flows inside in the tangential direction of thecathodes 20 and 22 and moves down while rotating along the inner side ofthe cathodes 20 and 22, in which some of the water solution isdischarged out of the conical part 15 through the outlet 16 and someflows into the hollow portion of the cathode 30 and is discharged up tothe outside. The water solution flowing inside in the tangentialdirection of the electrolytic cell having a cyclone shape is dischargedoutside through the anode while generating a rising current at the lowerportion inside the electrolytic cell.

The anode 30 and the cathodes 20 and 22 are electrically connected bythe water solution in the electrolytic cell, and metal ions such asgold, silver, and platinum is reduced by electrons from the cathodes andextracted in a solid state on the sub-cathode 22.

Metal can be effectively recovered through electrowinning in the relatedart, generally, when 3 g/L or more metal ions are in a water solution,but in the present invention, electrowinning is possible even at aconcentration of metal ions of 0.3 g/L or less and this is because themovement speed of metal ions is high due to the cyclone typeelectrolytic cell.

The water solution generates a turbulent flow in the electrolytic celland the generation of a turbulent flow can be found even from therelationship between a dimensionless Reynolds number (Re) showing a flowspeed and a dimensionless Sherwood number (Sh) showing mass transfer.

Generation of a turbulent flow is based on the inherent geometricalfeatures of a cyclone. In the turbulent flow, mass transfer of metalions rapidly increases. That is, a diffusion layer that is the distanceof diffusion of metal ions becomes thin, so the distance that the metalions diffuse to the surface of a cathode relatively decreases, andaccordingly, the reaction speed increases. Further, particularly, randomfluctuation of metal ions that is an inherent feature of a turbulent isgenerated, so the metal ions are suddenly moved to the surface of acathode and accordingly mass transfer is rapidly increased.

After the electrolysis, the water solution discharged through the outlet16 of the electrolytic cell 100 and the anode 30 is supplied to theassistant tank 200. The assistant tank 200 functions as a buffer betweenthe electrolyzer 100 and the solid-liquid separator 300. That is, itremoves stability in processes that may be caused by a differencebetween the flow rate through the pump 501 supplying a water solution tothe electrolyzer 100 and the flow rate through the pump 502 supplying awater solution to the solid-liquid separator 300 from the electrolyzer100.

The water solution in the assistant tank 200 is supplied to thesolid-liquid separator 300 by the second pump 502. Metal particles areseparated from the water solution in the solid-liquid separator 300 sothat only the liquid is supplied to the reservoir 400.

The metal electrodeposited on the assistant cathode 22 in theelectrolyzer 100 and the metal separated by the solid-liquid separator300 are recovered after the operation continues for a predetermined timeand then the process is stopped, and then the operation is startedagain.

In the process recovering metal described above, continuous operation isstably made by the assistant tank 200, so economic value is veryincreased. Further, metal that is easy to separate from the cathodes 20and 22 is effectively recovered by the solid-liquid separator 300 andcontinuous operation is stably performed. Further, it is possible toeffectively process a water solution having two or more components withdifferent recovery features simultaneously using the electrolyzer 100and the solid-liquid separator 300.

Operation when there is a problem with the level of the assistant tank200 and when the solid-liquid separator 300 is washed, which isdifferent from the process in the normal state described above, isdescribed hereafter.

The case when there is a problem with the level of the assistant tank200 is described first with reference to FIG. 10.

Even in a normal operation (S100), the flow rate of the assistant tank200 is the changed by the difference between the flow rates through thepumps 501 and 502. When the flow rate to the electrolyzer 100 is largerthan the flow rate to the solid-liquid separator 300, the level of theassistant tank 200 is continuously decreased, and in the opposite case,the level of the assistant tank 200 is continuously increased. When thedecreased level and the increased level become a predetermined level ormore, the assistant tank 200 cannot appropriately function as a buffer.

The controller 700 receives a level value from the level sensor 210 ofthe assistant tank 200 and determines whether the level is or notbetween a high level and a low level (5110).

When the level value is very low, under the low level, the controller700 stops the second pump 502 supplying a water solution to thesolid-liquid separator 300 (S120). Accordingly, the level of theassistant tank 200 increases. After a predetermined time passes, thecontroller 700 checks again the level, and when the level is between thehigh level and the low level, it performs the normal operation byoperating the second pump 502 (S140).

In another embodiment, the controller 700 can restart the pump 502, whenthe level of the assistant tank 200 becomes a predetermined levelbetween the low level and the high level (for example, 50%, 60%, and70%) after the second pump 502 is stopped. Further, it may be possibleto reduce the work flow rate without stopping the second pump 502.

When the level value is very high, over the high level, the controller700 stops the first pump 501 supplying a water solution to theelectrolyzer 100 (S130). Accordingly, the level of the assistant tank200 decreases. After a predetermined time passes, the controller 700checks again the level, and when the level is between the high level andthe low level, it performs the normal operation by operating the firstpump 501 (S140).

In another embodiment, the controller 700 can restart the first pump501, when the level of the assistant tank 200 becomes a predeterminedlevel between the low level and the high level (for example, 30%, 40%,and 50%) after the first pump 501 is stopped. Further, it may bepossible to reduce the flow rate without stopping the first pump 501.

In another embodiment, when the level of the assistant tank 200 is low,the controller 600 can increase of the flow rate through the first pump501 and decrease the flow rate through the second pump 502, and then thelevel of the assistant tank 200 is high, the controller can decrease theflow rate through the pump 501 and increase the flow rate through thepump 502. Further, this adjustment may be always performed so that thelevel of the assistant tank 200 is a predetermined level (for example,40%, 50%, and 60%).

As the level of the assistant tank 200 is controlled, as describedabove, the assistant tank 200 can keep stably functioning as a buffer,so the reliability of the continuous process is improved.

Next, the operation when the solid-liquid separator 300 is washed isdescribed with reference to FIG. 11.

During the normal operation, when the controller 600 determines that itis time to wash, washing is started. The controller 600 can determinethe start of washing at each predetermined operation time on the basisof time information received from the timer 800.

In another embodiment, the controller 600 can determine the start ofwashing on the basis of the pressure of the solid-liquid separator 300(washing is started when the pressure becomes a predetermined level ormore), and the metal concentration in a water solution may be consideredin determining the start of washing (washing is started earlier when themetal concentration is high).

When start of washing is determined, first, the first pump 501 forsupplying a water solution to the electrolyzer 100 and the first valve601 at the outlet of the assistant tank 200 are turned off (S210). Next,the second pump 502 for supplying a water solution to the solid-liquidseparator 300 and the second valve 602 at the outlet of the solid-liquidseparator 300 are turned off (S220). Accordingly, the flow of a watersolution is removed in the electrolyzer 100 and the solid-liquidseparator 300.

Next, the washing unit is started. In detail, the third valve 603connected to the washing water supplier, the second pump 502 connectedto the solid-liquid separator 300, and the fourth valve 604 connected tothe washing water discharger are turned on (S230). Accordingly, awashing process in which washing water is supplied from the washingwater supplier to the solid-liquid separator 300, washes thesolid-liquid separator 300, and then discharge to the washing waterdischarger is performed (S240).

When the washing is finished, the washing water supply is stopped byturning off the third valve 603, and the second pump 502 and the fourthvalve 604 are also turned off (S250). Accordingly, the washing watersupplier and the washing water discharger are separated from thesolid-liquid separator 300 and the operation of the washing unit isstopped.

After the washing process described above is finished, the normal stateoperation (S260) is performed.

The system for recovering metal described above may be changed invarious ways. In particular, a plurality of electrolyzers 100 and/or thesolid-liquid separators 300 may be provided to achieve stable operationand continuous operation.

When the electrolyzers 100 are provided in parallel and metalelectrodeposited by any one of the electrolyzers 100 is recovered, acontinuous process can be maintained by another electrolyzer 100.

When the solid-liquid separators 300 are provided in parallel and anyone of the solid-liquid separators 300 is washed or metal is recoveredfrom a filter, the continuous process can be maintained by anothersolid-liquid separator 300.

The recovery behavior of recovering metal depends on the area ratio ofanode/cathode.

A recovery behavior according to an area ratio of anode/cathode isdescribed with reference to FIGS. 12 and 13.

In order to observe the recovery behavior according to the area of ananode, the area ratio of anode/cathode was changed to 0.42, 0.55, 0.67,0.79, 0.93, and 1.02 by changing the area of the anode. The material ofthe anode was SUS 304, the flow rate was fixed to 7.7 M/s (145 LPM), andthe total applied current was 51.3 A, twice the electrorefiningreference current density (550 A/e).

FIG. 12 shows a behavior when Au is recovered. The concentration ofremaining gold linearly decreased to about 50 ppm, but thereafter, thereduction largely decreased, so the recovery efficiency is likedecreasing while the earlier recovery efficiency is high and theremaining concentration of the gold lowers. When the area ratio ofanode/cathode was smaller than 1.0, the remaining concentration of thegold after about 10 minutes passed was 140˜160 ppm, whereas when thearea ratio was larger than 1, the concentration was 107.6 ppm.Accordingly, it was found that the area ratio of anode/cathode waslarger than 1.0, the earlier recovery ratio was excellent. When the arearation of anode/cathode is larger than 1 even after about 22 minutespassed, a recovery behavior that the remaining concentration of the goldwas 28.7 ppm, which was more excellent than 48 to 70 ppm in other cases.However, after 45 minutes passed, the remaining concentration of thegold was 5.1 ppm to 9.1 ppm, so the difference of the recovery ratio waslargely decreased.

FIG. 13 shows a recovery behavior when the area ratio of anode/cathodewas 0.93 and 1.02 and the process time was increased up to 180 minutes.Similar to the result shown in FIG. 12, when the area ratio was largerthan 1, the earlier recovery ratio was excellent, but it almostconverged after 45 minutes. Further, when 180 minutes was reached, theremaining concentration of the gold decreased to 1.3 ppm for the arearatio of 1.02 and to 3.3 ppm for the area ratio of 0.93.

From this result, it could be found that the area ratio of anode/cathodeis preferably larger than 1 to increase the earlier recovery ratio. Indetail, the area ratio of anode/cathode may be 1 to 1.5 or 1 to 1.2

The configuration of a cathode according to a second embodiment isdescribed in detail with reference to FIG. 14.

In the second embodiment, a cathode connection hole 21 a correspondingto the connection hole 14 of the body 11 is formed at the main cathode20. The sub-cathode 22 can be connected directly to a power through theconnection hole 14 and the cathode connection hole 21 a.

The configuration of a cathode according to a third embodiment isdescribed in detail with reference to FIG. 15.

In the third embodiment, the sub-cathode 22 is formed in a cylindricalshape. Accordingly, it can be quickly inserted into the main cathode 20.When metal is recovered after a process, the sub-cathode 22 may be cutinto a plate shape, if necessary.

The configuration of a cathode according to a fourth embodiment isdescribed in detail with reference to FIG. 16.

In the fourth embodiment, projections 24 are formed on the surface ofthe sub-cathode 12 that is brought in contact with the main cathode 20.The sub-cathode 22 can be more surely electrically connected to the maincathode 20 by the projections 24. The projections 24 may be changed intovarious shapes and arrangements, for example, into the shape of a lineor a lattice.

A recovery behaviors according to the materials of an anode aredescribed with reference to FIGS. 17 and 18. FIG. 17 shows recoverybehaviors when an anode coated with platinum and an SUS anode are used.Tests were performed under the condition that the area ratio ofanode/cathode was 1.02 and the flow rate and the applied current werethe same as those described with reference to FIGS. 12 and 13. Theremaining concentration of gold converged to 1.3 ppm to 1.8 ppm at thetwo kinds of anodes. FIG. 18 is an enlarged graph of the earlier stagefor observing the earlier recovery behavior.

The anode coated with platinum looks light have a slightly largerrecover ratio at the earlier stage of the test, but it was found thatthere is little difference from the earlier stage in the recoverybehavior. However, the surfaces of the anodes observed after the testwere considerably different. That is, as for the SUS anode, there wasconsiderable corrosion on the surface, so it is expected to have anadverse influence on the purity of the recovered gold. As for the anodecoated with platinum, elution was maximally suppressed and the purity ofthe gold maintained almost at 100%.

Recovery behaviors according to applied currents are described withreference to FIG. 19.

Total currents of 38.5 A, 51.3 A, and 76.9 A were applied with respectto the area of an anode, by selecting 1.5 times, two times, and threetimes the electrorefining reference current density. In the tests, whena current of 76.9 A was applied, resistant heat was generated too muchat the joint of the anode and the cathode, so a portion of ahydrocyclone was melted. Accordingly, the test for the current wasstopped and recover behaviors under the other conditions were shown inFIG. 19. After 20 minutes passed, the remaining concentration of thegold was 26.4 ppm when the current was 51.3 A, and when the current islow at 38.5 A, the remaining concentration was 34.0 ppm, lower than thatfor the current of 51.3 A, but then, the convergence concentration wasalmost similar. That is, in the test for 180 minutes, the remainingconcentrations were 1.5 ppm and 1.7 ppm, in which there is littledifference.

Considering only the recovery ratio of the gold, it is important toincrease the current density, but considering the entire energyconsumption efficiency, it is considered that it is preferable toperform recovering at a high speed under applied current of 35 A to 45A.

FIG. 20 is a graph showing recovery behaviors according to flow rates.

Recovery behaviors at flow rates of 5.3 m/s (100 LPM) and 7.7 m/s (145LPM) were observed. Similar to the tests with different currentdensities, in this case, the recovery ratio behaviors were differentonly at the earlier stages of the tests. That is, the remainingconcentration of gold at the flow rate of 7.7 m/s was 26.4 ppm and 4.1ppm, respectively, after 22 minutes and 45 minutes passed, and was 45.4ppm and 6.3 ppm at 5.3 m/s. After 180 minutes passed, the remainingconcentration was 1.5 ppm and 1.6 ppm, so it can be found that as thetime passes, the recovery ratio behaviors become similar and converge tothe same value.

The recovery ratio behavior according to a change in applied current andthe recovery ratio behavior according to a change in flow rate showsimilar tendencies, but when the earlier recovery ratio is important, itis considered that it is more effective to increase the flow rate ratherthan the applied current.

Although the present invention has been described with reference to theexemplary embodiments illustrated in the drawings, those are onlyexamples and may be changed and modified into other equivalent exemplaryembodiments from the present invention by those skilled in the art.Therefore, the actual protection range of the present invention shouldbe determined only by the accompanying claims.

What is claimed is:
 1. A reactor for recovering metal, comprising anelectrolyzer that receives a water solution containing metal ions fromthe outside and reduces and extracts metal ions in the water solution onthe surface of cathodes, when the water solution is supplied into areaction space between an anode and the cathodes surrounding the anode,wherein the cathodes include a main cathode and a sub-cathode disposedinside the main cathode and separable from the main cathode.
 2. Thereactor of claim 1, wherein the reduction and extraction of the metalions occur on the inner side of the sub-cathode.
 3. The reactor of claim1, wherein the main cathode has a ring shape and the sub-cathode has aplate shape and is wound inside the main cathode.
 4. The reactor ofclaim 1, wherein the sub-cathode is made of a material that is dissolvedby acid that does not dissolve metal to be recovered.
 5. The reactor ofclaim 1, wherein the sub-cathode is in close contact with the maincathode and substantially fully covers the inner side of the maincathode.
 6. The reactor of claim 1, wherein the anode is formed in a barshape and has a plurality of grooves on the outer side.
 7. The reactorof claim 1, wherein the anode is a hollow part with both ends open andthe side of the anode is not open.
 8. The reactor of claim 1, whereinthe ratio of the surface area of surface area/cathode of the anode inthe reaction space is larger than
 1. 9. A system for recovering metal,comprising a reservoir that keeps a water solution containing metalions; and an electrolyzer that receives the water solution from theoutside and reduces and extracts metal ions in the water solution on thesurface of cathodes, when the water solution is supplied into a reactionspace between an anode and the cathodes surrounding the anode, whereinthe cathodes include a main cathode and a sub-cathode disposed insidethe main cathode and separable from the main cathode.
 10. The system ofclaim 9, wherein the sub-cathode substantially fully covers the innerside of the main cathode in close contact with the main cathode, and thereduction and extraction of the metal ions occur on the inner side ofthe sub-cathode.
 11. The reactor of claim 9, wherein the sub-cathode ismade of a material that is dissolved by acid that does not dissolvemetal to be recovered.
 12. The reactor of claim 9, wherein the anode isformed in a bar shape and has a plurality of grooves on the outer side.13. The reactor of claim 9, wherein the anode is a hollow part with bothends open and the side of the anode is not open.
 14. The reactor ofclaim 9, wherein the ratio of the surface area of surface area/cathodeof the anode in the reaction space is larger than
 1. 15. The system ofclaim 9, further comprising a solid-liquid separator that receives awater solution discharged from the electrolyzer and separates metalparticles.
 16. The system of claim 15, further comprising: an assistanttank that is disposed between the electrolyzer and the solid-liquidseparator; and a controller that reduces a water solution supplied tothe electrolyzer when the level of the assistant tank is a first levelor more, and that reduces the water solution supplied to thesolid-liquid separator when the level of the assistant tank is a secondlevel, which is smaller than the first level, or less.